Papers by Keyword: Thixojoining

Abstract: The application of hybrid structures or components made of dissimilar metal offers the potential to utilize the advantages of different materials often providing unique solutions to engineering requirements. However, the joining of materials by conventional welding techniques becomes difficult if the physical properties such as melting temperature and thermal expansion coefficients of the two materials are different. In this study, a new process of joining semi-solid AISI D2 tool steel and AISI 304 stainless steel using a partial remelting method is proposed. Moreover, the effect of the holding time on the microstructural evolution was investigated. The processing temperatures for the thixojoining was 1320°C and held for 5, 12, 20 and 30 minutes, respectively. The results obtained from investigating the basic geometries demonstrated a good joining quality that differs from the conventional process of welding. Metallographic analyses along the joint interface between semi-solid AISI D2 and 304 stainless steel showed a smooth transition from one to the other, with neither oxides nor microcracking being observed.

Abstract: In many circumstances, a high quality joint of dissimilar metals can be hardly achieved by conventional welding process. In this study, a new process of joining semi-solid AISI D2 tool steel and AISI 304 stainless steel using a partial remelting method is proposed. The differences of two dissimilar steels at the test temperature on microstructural developments across the interface joint area were investigated. After Thixo-Joining, Interfacial microstructures were examined by optical microscope and scanning electron microscope (SEM) equipped with EDS (energy dispersive spectroscopy) in order to verify the interface welded area during the joining process while X-ray phase analysis was performed to identify the phase evolution and the type of carbides. The experimental results showed that at 1300°C a full penetration welded joint can also be clearly seen, whereby the base metal (D2 tool steel) is connected to the insert metal (304 stainless steel) along the bonding boundary to achieve what appears to be a perfect joining at the interfaces of both metals.

Abstract: Cold-work tool steel is considered to be a non-weldable metal due to its high percentage content of carbon and alloying elements. To address this problem the application of a new process of semisolid joining using a direct partial remelting method was developedto achieve a spherical join structure between two parts of AISI D2 cold-work tool steel. Since the surface oxidation of this metalis very high, the control of the atmosphere during joining had to be considered. Samples were heated in an argon atmosphere at two different temperatures of 1250°C and 1275°C for 10 minutes. Metallographic analyses along the joint interface showed that an increase in temperature promoted the final joining properties and also that at a liquid fraction of 15% joining was not fully practicable. However, a20% liquid fraction can produce a very good joint and microstructure as compared to the other experimental liquid fraction. Metallographic analyses along the joint interface showed a smooth transition from one to the other and neither oxides nor microcracking was observed. The current work confirmed that avoidance of a dendritic microstructure in the semisolid joined zone and high bonding quality components can be achieved without the need for force or complex equipment when compared to conventional welding processes.

Abstract: At the Institute of Metal Forming (IBF) current investigations within the framework of the Collaborative Research Centre 289 are mainly concentrated on forming of semi-solid precursor material of the steel grades X210CrW12 and 100Cr6. One important task is the precise temperature for the composition of solid and liquid phase fraction in the preheated billet. Experimental measurements and numerical simulations show significant heat losses during transport of the billet and after its insertion into the die. These developing temperature gradients influence strongly the resulting temperature field in the formed component. In case of the forming tools the critical increase of the temperature depending on the tool material is shown. As fundamental research in the field of thixojoining the temperature development of the inserts is analysed and demonstrates the feasibility of joining higher and lower melting materials into the semi-solid matrix.

Abstract: The thixoforming processes join the advantages of conventional forming technologies as forging and casting in respect of the mechanical properties and the practicable geometries. Within the framework of the Collaborative Research Centre 289 at the RWTH Aachen University intensive investigations on semi-solid processing with some steel grades have been running. For this purpose an automated thixoforging plant (thixo-cell) has been developed in a closed cooperation with several industrial partners. With this equipment multi material demonstrator components have been successfully produced by thixojoining using semi-solid X210CrW12 tool steel.